Inner fin for heat exchanger flat tubes and evaporator

ABSTRACT

The present invention relates to an inner fin  5  for heat exchanger flat tubes  22 A which comprises a metal plate having a corrugated cross section and which is to be enclosed in the flat tube  22 A, all ridges  51  and all furrows  52  of the inner fin being joinable to an inner surface of the flat tube  22 A by brazing. At least one of the ridges  51  and the furrows  52  of the inner fin  5  is provided with a turbulence promoting protrusion  53  facing toward a side opposite to the side to be brazed. The turbulence promoting protrusion  53  is so sized that a clearance to be created between a caved portion  54  formed on a rear side of the protrusion and the inner surface of the flat tube  22 A can be filled with a brazing material  6.  A fluid to be passed through the flat tube  22 A is caused to flow in a more turbulent state by the protrusion  53  to thereby achieve an improved heat transfer efficiency.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is an application filed under 35 U.S.C. §111(a)claiming the benefit pursuant to 35 U.S.C. §119(e)(1) of the filing dataof U.S. Provisional Application No. 60/302,654 filed Jul. 5, 2001pursuant to 35 U.S.C. §111(b).

TECHNICAL FIELD

[0002] The present invention relates to inner fins for heat exchangerflat tubes, and to evaporators which are adapted, for example, for useas those for motor vehicle air conditioners and which have incorporatedtherein such inner fins.

BACKGROUND ART

[0003] In evaporators for motor vehicle air conditioners, it hasheretofore been practice to arrange inner fins in flat tubes to give anincreased heat transfer area to the refrigerant and thereby achieveimproved performance.

[0004] Already known as such an inner fin is one comprising a metalsheet of corrugated cross section and enclosed in a flat tube. The innerfin has all ridges and furrows thereof brazed to the inner surface ofthe flat tube.

[0005] The inner fin described has been given an increased heat transferarea by diminishing the spacing between the ridges and the furrows,i.e., the fin pitch, whereas difficulties are encountered in fabricatinginner fins having a further decreased fin pitch. It has also been foundthat if realized, further diminished fin pitches are unable to achievecorrespondingly improved effects.

[0006] An object of the present invention is to provide an inner fin forheat exchanger flat tubes which comprises a metal sheet of corrugatedcross section and which is adapted to achieve a further improved heattransfer efficiency without diminishing the fin pitch. Another object ofthe invention is to provide an evaporator wherein the above inner fin isused and which is thereby improved in performance.

DISCLOSURE OF THE INVENTION

[0007] The present invention provides an inner fin for heat exchangerflat tubes which comprises a metal plate having a corrugated crosssection and which is to be enclosed in the flat tube, all ridges and allfurrows of the inner fin being joinable to an inner surface of the flattube by brazing, the inner fin being characterized in that at least oneof the ridges and the furrows is provided with a turbulence promotingprotrusion facing toward a side opposite to the side to be brazed, theturbulence promoting protrusion being so sized that a clearance to becreated between a caved portion formed on a rear side of the protrusionand the inner surface of the flat tube can be filled with a brazingmaterial.

[0008] When at least one of all the ridges and all the furrows of theinner fin is provided with a turbulence promoting protrusion facingtoward a side opposite to the side to be brazed, the fluid to be passedthrough the flat tube wherein the inner fin is enclosed is caused toflow in a more turbulent state by the protrusion to thereby achieve ahigher heat transfer efficiency. Moreover, since the turbulencepromoting protrusion is so sized that the clearance to be createdbetween the caved portion formed on the rear side of the protrusion andthe inner surface of the flat tube can be filled with a brazingmaterial, a plurality of fluid channels formed within the flat tube bythe inner fin and arranged in parallel widthwise of the tube areprevented from communicating with one another and will not involveincreased flow resistance. The inner fin of the invention for heatexchanger flat tubes is therefore improved in heat transfer efficiencyby the turbulence promoting protrusion without reducing the fin pitch.

[0009] The turbulence promoting protrusion produces the secondary effectto be described below. While many of such inner fins, which are madefrom a metal sheet, are temporarily stored as arranged one above anotherin the form of a stack, the fins are difficult to separate if held inintimate contact with one another, possibly causing trouble inassembling heat exchangers. If the inner fins are provided with suchprotrusions, the inner fins are held out of intimate contact with oneanother even when stacked up in a large number. The inner fins are theneasy to take out one by one from the stack to ensure a high efficiencyin assembling heat exchangers. From the viewpoint of the intimatecontact preventing effect, it is desired that the protrusions be formedin ridges and/or furrows at least in the vicinity of opposite edges ofthe inner fin, whereby fins are made easy to separate one by one even ifstacked up in a large number.

[0010] With the inner fin of the invention for heat exchanger flattubes, the turbulence promoting protrusion has a dimension of 1 to 1.5mm longitudinally of the inner fin and a height of 0.2 to 0.4 mm.

[0011] If the protrusion measures less than 1 mm longitudinally of theinner fin and less than 0.2 mm in height, such turbulence as willcontribute to an improvement in heat transfer efficiency will not occurin the fluid. On the other hand, if the protrusion measures more than1.5 mm along the length of the inner fin and in excess of 0.4 mm inheight, there is the possibility of failing to fill up the clearancebetween the caved portion on the rear side of the protrusion and theinner surface of the flat tube with the brazing material, and excessiveflow resistance will then be offered.

[0012] Turbulence promoting protrusions may be provided randomly withrespect to the widthwise direction of the inner fin, or may be formed ata predetermined interval, for example, in every three furrows. One or aplurality of turbulence promoting protrusions may be formed in one ridgeor furrow. When to be provided, a plurality of protrusions may bearranged with a definite pitch or randomly. When a plurality ofprotrusions are to be formed in one ridge or furrow, there is a need todetermine the number and pitch of protrusions so as to avoid excessiveflow resistance.

[0013] The inner fin is prepared usually by roll forming. In this case,the protrusion can be formed simultaneously with the forming of theinner fin itself by using a pair of forming rolls having a projectionand a cavity respectively at corresponding portions.

[0014] The flat tube for use in heat exchangers for enclosing thereinthe inner fin of the invention is not limited particularly but can be,for example, an electric resistance welded tube, or a flat tubularportion comprising a pair of dishlike plates each having a flat tubeforming portion and joined to each other face-to-face. In the lattercase, the inner fin of the invention is disposed in each of two flattubular portions formed by a pair of dishlike plates each of which has apartition ridge and flat tube forming portions at opposite sides of thepartition ridge and which are joined to each other as arrangedface-to-face. The two inner fins may have adjacent edges which are madeintegral with each other by a joint portion, which is interposed betweenthe partition ridges of the two dishlike plates.

[0015] The ridges and the furrows of the inner fin are brazed to theinner surface of the flat tube, for example, by preparing at least oneof the inner fin and the flat tube from a brazing sheet and using thebrazing material cladding the sheet surface. Usually, however, the flattube only is made from the brazing sheet.

[0016] The present invention further provides an evaporator comprising aplurality of flat tubes, each of the flat tubes having enclosed thereinthe inner fin of the invention, the inner fin having all the ridges andall the furrows thereof brazed to the inner surface of the flat tube.

[0017] The turbulence promoting protrusions of the inner fins improvethe efficiency of heat exchange between the refrigerant flowing throughthe flat tubes and the air to be cooled and flowing externally of theflat tubes, consequently enabling the evaporator to exhibit outstandingperformance.

[0018] The evaporator according to the invention can be a layeredevaporator comprising flat tubes which are provided by flat tubularportions formed by pairs of dishlike plates each having a flat tubeforming recessed portion, the pair of dishlike plates being joined toeach other as arranged face-to-face.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a perspective view showing an embodiment of theinvention, i.e., a layered evaporator for motor vehicle airconditioners.

[0020]FIG. 2 is a perspective view showing two dishlike platesconstituting a tube element, and an inner fin to be provided inside ofthese plates.

[0021]FIG. 3, (a) is a side elevation of the inner fin, and (b) is across sectional view of the inner fin.

[0022]FIG. 4, (a) is an enlarged fragmentary view in cross sectionshowing the inner fin as enclosed in a flat tubular portion, and (b) isan enlarged fragmentary view in longitudinal section taken along theline b-b in (a).

[0023]FIG. 5 shows another embodiment of the invention; (a) being a sideelevation of an inner fin, (b) being a view in cross section of theinner fin.

BEST MODE OF CARRYING OUT THE INVENTION

[0024] FIGS. 1 to 4 show an embodiment of the present invention. Theillustrated embodiment is suitable for use in layered evaporators formotor vehicle air conditioners.

[0025]FIG. 1 shows the entire layered evaporator for motor vehicle airconditioners. The evaporator 1 has an evaporator core 10 comprising aplurality of tube elements 2, 2A which are joined to one another byouter fins 3 and each of which comprises a pair of dishlike plates 20,20A facing and joined to each other. The evaporator core 10 comprises aplurality of front flat tubular portions 22A arranged side by sidelaterally, a plurality of rear flat tubular portions 22A arranged sideby side laterally, a front upper header 22B and a front lower header 22Bfor interconnecting the upper ends' and lower ends of the front flattubular portions 22A in communication, and a rear upper header 22B and arear lower header 22B for interconnecting the upper ends and lower endsof the rear flat tubular portions 22A in communication, these componentsbeing provided by the tube elements 2 other than the tube element at theleft end. The tube element 2A at the left end has a refrigerant inletpassageway 201 and a refrigerant outlet passageway 202. Attached to theouter side of this tube element 2A is a pipe coupling block 4 having arefrigerant inlet pipe connecting opening 41 and a refrigerant outletpipe connecting opening 42. Partition walls (not shown) are provided inthe headers 22B at required portions thereof. Via the inlet pipeconnecting opening 41 and the inlet passageway 201, a refrigerant flowsinto the left end of the rear upper header 22B, then flows through allthe headers 22B and the flat tubular portions 22A in a predeterminedpattern, thereafter flows out of the left end of the front upper header22B and is discharged via the outlet passageway 202 and the outlet pipeconnecting opening 42.

[0026]FIG. 2 shows two dishlike plates 20 constituting each of the tubeelements 2 other than the element 2A at the left end, and inner fins 5enclosed with these plates 20. The dishlike plates 20 are prepared froma blazing sheet clad with a brazing material over opposite surfacesthereof. Each dishlike plate 20 has a vertical partition ridge 21 at thewidthwise center portion thereof to provide flat tube forming recessedportions 22 respectively at the front and rear sides of the ridge 21.The dishlike plate 20 further has header forming recessed portions 23integral with the upper and lower ends of the front and rear flat tubeforming recessed portions 22. A refrigerant passage aperture 24 isformed in the bottom wall of the recessed portion 23. However, noaperture 24 is formed in the bottom walls of required header formingrecessed portions 23 of some dishlike plates 20. These bottom wallsprovide partition walls. The two dishlike plates 20 are jointed to eachother face-to-face, whereby front and rear two flat tubular portions 22Aare formed. Two inner fins 5 are arranged respectively in these twotubular portions 22A and are those embodying the present invention. Thetwo inner fins 5 have adjacent edges which are made integral with eachother by a joint portion 50 which is interposed between the partitionridges 21 of the two dishlike plates 20.

[0027] With reference to FIGS. 2 to 4, the inner fin 5 of the presentinvention comprises an aluminum alloy sheet having a corrugated crosssection and formed by roll forming. The inner fin 5 is enclosed in theflat tubular portion 22A and all ridges 51 and all furrows 52 are joinedto the inner surface of the flat tubular portion 22A by brazing. Theinner fin 5 forms a plurality of refrigerant channels 221 arranged sideby side from the front rearward in the interior of the tubular portion22A. As shown in FIGS. 3 and 4, a plurality of furrows 52 of the innerfin 5 are provided with turbulence promoting protrusions 53 facingtoward a direction opposite to the brazed side of these furrows.

[0028] Such inner fins 5 are formed by cutting an aluminum alloy sheetof corrugated cross section into specified lengths, and thereaftertemporarily stored as stacked up in layers. In this state, the adjacentinner fins 5 are held out of intimate contact with each other due to thepresence of turbulence promoting protrusions 53. Accordingly, the innerfins 5 can be taken out one by one from the stack easily to ensureefficient work in assembling the evaporator 1.

[0029] In each of the front and rear inner fins 5 shown in FIG. 3, thefurrows 52 provided with turbulence promoting protrusions 53 are five innumber. This number corresponds to about one fifth of the combinednumber (=23) of all ridges 51 and all furrows 52 of the fin. The fivefurrows 52 provided with the protrusions 53 are arranged randomly withrespect to the widthwise direction of the inner fin as seen in FIG. 3.Each of the five furrows 52 has one to five protrusions 53.

[0030] With reference to FIG. 4, (b), a clearance created between acaved portion 54 formed on the rear side of the protrusion 53 and theinner surface of the flat tubular portion 22A is filled with a brazingmaterial 6. [The brazing material is not shown in FIG. 4, (a).] Theturbulence promoting protrusion 53 is 1 mm in dimension A along thelength of the inner fin and 0.4 mm in height B.

[0031] With the evaporator 1 described above, the refrigerant flowingthrough the refrigerant channels 221 within the flat tubular portion 22Ais in a boiling state and therefore usually turbulent, whereas theturbulence promoting protrusions 53 formed in the inner fin 5 produce agreater turbulent flow to thereby achieve an improved heat transferefficiency. The refrigerant flows straight through each refrigerantchannel 221 without deflecting into other channel 221. This results indiminished resistance to the flow.

[0032]FIG. 5 shows another embodiment of the invention. With referenceto FIG. 5, each of front and rear inner fins 5 made integral with eachother by a joint portion 50 has turbulence promoting protrusions 53which are formed in three furrows 52 positioned in the vicinity of thefront and rear edges of the fin. One to three protrusions 53 are formedin each of the three furrows 52. With the exception of this feature, thesecond embodiment is the same as the first embodiment shown in FIGS. 1to 4.

[0033] The embodiments described above are merely illustrative examples.The present invention can of course be practiced as suitably modifiedwithout departing from the gist of the invention as set forth in theappended claims.

[0034] Industrial Applicability

[0035] As described above, the present invention is useful for improvingthe efficiency of heat exchangers which comprise flat tubes having innerfins arranged therein. The invention is useful especially for improvingthe efficiency of evaporators such as those for motor vehicle airconditioners.

1. An inner fin for heat exchanger flat tubes which comprises a metalplate having a corrugated cross section and which is to be enclosed inthe flat tube, all ridges and all furrows of the inner fin beingjoinable to an inner surface of the flat tube by brazing, the inner finbeing characterized in that at least one of the ridges and the furrowsis provided with a turbulence promoting protrusion facing toward a sideopposite to the side to be brazed, the turbulence promoting protrusionbeing so sized that a clearance to be created between a caved portionformed on a rear side of the protrusion and the inner surface of theflat tube can be filled with a brazing material.
 2. An inner fin forheat exchanger flat tubes according to claim 1 wherein the turbulencepromoting protrusion has a dimension of 1 to 1.5 mm longitudinally ofthe inner fin and a height of 0.2 to 0.4 mm.
 3. An evaporator comprisinga plurality of flat tubes, each of the flat tubes having enclosedtherein an inner fin according to claim 1 or 2, the inner fin having allthe ridges and all the furrows thereof brazed to an inner surface of theflat tube.
 4. An evaporator according to claim 3 wherein the flat tubesare provided by flat tubular portions formed by pairs of dishlikeplates, each pair of dishlike plates facing and being joined to eachother.